1. Field of the Invention
The present invention relates to an image forming apparatus which uses an electrophotographic process, and which is provided with a cleaning blade to rub and remove toner or the like adhering to a surface of an image bearing member. The invention also relates to a process cartridge which is detachably mountable on such image forming apparatus.
2. Related Background Art
FIG. 5 is a schematic view which shows the conventionally used apparatus, in which several image formation means of an image forming apparatus that uses the electrophotographic process are compactly arranged to be of cartridge type. In FIG. 5, a reference numeral 1 designates a photosensitive drum serving as an image bearing member; 2 denotes a charging roller using the charging electrodes that is in contact with the surface of the photosensitive drum 1 for charging the photosensitive drum 1 uniformly; 5 denotes developing means for forming toner images by enabling toner to adhere to the electrostatic latent images formed on the surface of the photosensitive drum 1; and 8 denotes cleaning means for removing and collecting the toner remaining on the surface of the photosensitive drum 1. The photosensitive drum 1, the charging roller 2, the developing means 5, the cleaning means 8, and others are integrally supported by a housing 9 to be arranged in the form of a cartridge, thus structuring a process cartridge 11 altogether.
The developing means 5 rotates in the direction indicated by an arrow b, which is provided with a development sleeve 3 that carries toner, and a developing blade 4, which regulates the thickness of the toner layer on the development sleeve 3.
Below the photosensitive drum 1, a transfer roller 10 is arranged as transfer means for electrostatically transfer the developed images on the photosensitive drum 1 to a transfer material by charging the transfer material.
The transfer material P, which bears the non-fixed toner image transferred by the transfer roller 10, is conveyed to a fixing device (not shown), in which the non-fixed toner image is fixed by the application of heat and pressure by fixing means.
The cleaning means 8 is provided with a cleaning blade 6, which is supported by a supporting member 13, for scraping off the remaining toner after transfer from the photosensitive drum 1, and a receiving sheet 7 for catching and collecting the remaining toner after transfer thus scraped off. Also, on each of both end portions of the cleaning blade 6, a blade edge seal (not shown), such as foaming poly urethane, is arranged between the blade 6 and a container of the cleaning means 8.
Usually, the urethane rubber is often used for the cleaning blade 6, because the urethane rubber has a good durability.
Also, the urethane rubber has a high contactness and a high toner scraping capability, but its sliding performance is not good against the member with which the urethane rubber is in contact due to such excellent a contactness. Also, when the photosensitive drum 1 rotates, the cleaning blade 6 receives a force in the direction indicated by an arrow F in FIG. 5. However, since the cleaning blade is in contact with the surface of the photosensitive drum 1 in a direction counter to a rotational direction of the photosensitive drum 1, there is a problem of the so-called "blade turning up phenomenon" resulting from an evagination of an edge portion of the blade 6 turned in the direction indicated by the arrow F along with the rotational movement of the photosensitive drum 1 if the friction force becomes too strong between the photosensitive drum 1 and the blade 6.
Here, therefore, in order to deal with such problem, there is adopted a method for enhancing the lubricity by coating fine particles of silicon resin or fluoric particles as a lubricant on the contact portion of the eleaning blade 6 with the photosensitive drum 1. However, the lubricant is peeled off from the cleaning blade 6 and gradually reduced when the blade is used for a long time. Therefore, it is impossible to maintain the preventive effect of the blade turning up for a long time.
The following method is also known as another example of dealing with a problem of this kind.
Usually, the surface of the photosensitive drum 1 is almost in a mirror-like state due to its manufacture. Therefore, the cleaning blade 6 tends to be closely in contact with the photosensitive drum 1 to create an extremely large friction resistance. However, within a range that does not create any problem with respect to the image formation, the surface of the photosensitive drum may be made rough so as to reduce the area of contact between the cleaning blade 6 and the photosensitive drum 1. Then, the friction force can be reduced accordingly. In such a manner, the surface of the photosensitive drum 1 is made rough to a certain extent to prevent the friction force between the photosensitive drum 1 and the blade 6 from becoming excessive.
For example, in the specifications of Japanese Patent Application Laid-Open No. 08-095258 and Japanese Patent Application Laid-Open No. 11-002910, it is disclosed that the surface of the photosensitive drum 1, which is in contact with near the end portion of the blade, is made rougher than the surface of the central portion of the photosensitive drum 1.
This treatment is required in order to prevent noises from being generated by the vibrations of the cleaning blade 6, which is in contact with the end surface of the photosensitive drum 1, and also, to prevent the blade 6, from being turned up, because the side end, portion of the cleaning blade 6 which is a free end is easier to be turned up than the central portion thereof. In other words, the surface of the photosensitive drum 1 is made rough to a certain extent to reduce the area of contact between the cleaning blade 6 and the photosensitive drum 1 to make the friction force smaller. In this way, it becomes possible to prevent the friction force between the photosensitive drum 1 and the blade 6 from becoming excessive.
Further, in the specification of Japanese Patent Application Laid-Open No. 10-340027, a polishing member is disclosed as the one used for making the surface roughness greater on the end portion of the image bearing member 1 than that on the central portion thereof by making the polishing properties different for the polishing portion at the end where the end of the image bearing member 1 is polished in the width direction and the polishing portion in the center where the central portion of the image bearing member is polished.
For this disclosure, too, the polishing member is provided on purpose to make the surface of the photosensitive drum rough as is in the case described earlier, because the side end portion of the cleaning blade 6 is free, and for that matter, it is easier to be turned up than the central portion.
Further, in the specification of Japanese Patent Application Laid-Open No. 62-182785, it is disclosed that is developed on the ends of the photosensitive drum 1 in the wide direction of the sheet so that the talc is removed together with the toner from the surface of the photosensitive drum 1 or that the toner polishes the surface of the photosensitive drum 1 to remove the talc from the surface of the photosensitive drum 1 to avoid a smeared image.
This is the method for polishing the surface of the photosensitive drum 1 within the area of the development, which is evidently different from the means for polishing the surface of the photosensitive drum 1 outside the area of the development in accordance with the present invention.
However, there are problems encountered as given below as to such methods as disclosed in the specifications of Japanese Patent Application Laid-Open No. 08-095258 and Japanese Patent Application laid-Open No. 11-002910 that the blade turning up and others are prevented by making the surface of the photosensitive drum 1 rough in advance.
When the photosensitive drum is used for a long time, the surface thereof is ground gradually, and the surface roughness becomes smaller than that initially provided. Then, there is a possibility that the end portion of the blade 6 turns up eventually.
In other words, only with the roughness provided for the surface in advance, the blade turn up is encountered inevitably if the photosensitive drum is used for a long time.
Also, the method, in which the roughness of the end portion is made greater by polishing the surface of the photosensitive drum 1 by use of the polishing member as disclosed in the specification of Japanese Patent Application Laid-Open No. 10-340027, makes it possible to maintain the roughness of the end portion to a certain extent, and continuously prevent the blade 6 from being tuned up. However, if contact charging means 2 is adopted as in the case of the present invention, the charging defect may take place eventually, because polished particles are allowed to adhere to the contact charging means 2 when the polishing member is positioned on the downstream side of the cleaning means in the operating direction of the photosensitive drum 1.
Also, since the charging member 2 is the charging roller 2, which serves as a contact charging member, this charging roller is pressed by springs (not shown) on both end portions so that it is in contact with the surface of the photosensitive drum 1. Then, this charging roller is rotated by the rotation of the photosensitive drum 1. In other words, both end portions are higher than the central potion. Therefore, the surface material of the charging roller 2 is rubbed and transferred to the surface of the photosensitive drum 1, although in a limited quantity. This may take place particularly on both end portions. This condition makes it difficult for the surface of the photosensitive drum 1 to slide easily, and leads to inviting the turning up of the blade 6 eventually.
Then, on the locations other than the end portions, the transfer roller 10 is in contact with the surface of the photosensitive drum 1 in particular. The transfer roller 10 itself cleans the surface of the photosensitive drum 1. Further, on the inner side thereof, the toner images and the transfer material P are in engagement with cleaning. In other words, sliding becomes more difficult particularly only on the surface of the photosensitive drum 1 where the charging roller 2 is in contact on the outer side than the portion where the transfer roller 10 is in contact. This motivates the turning up of the blade.